1. Field of the Invention
Apparatus for treatment of stormwater runoff through volume-control-based detention and minimization of pollutant remobilization.
2. Description of the Related Art
This invention relates generally to liquid purification and separation and, more specifically, to an apparatus for separation of pollutants in urban stormwater runoff from the runoff water. This apparatus utilizes gravitational separation and tortuosity, resulting from a plurality of baffles both perpendicular to and oblique to the primary water flow direction, to trap substances less-dense and more-dense than water. This invention is differentiated from prior art by improved resistance to pollutant remobilization, resulting from an iterative experimental hydraulic design process. In addition, this invention provides a degree of retention through volume-control that exceeds that provided by existing gravitational, sub-surface, stormwater treatment systems.
Impacts of stormwater runoff on receiving environments have been documented extensively in engineering and scientific literature. Section 402 of the Federal Clean Water Act (CWA) regulates stormwater discharges through the National Pollutant Discharge Elimination System (NPDES). Treatment of stormwater runoff using best management practices (BMPs) is a typical requirement of state and local regulations, as well. In the 1990s, there has been growing interest in xe2x80x98ultra-urban/space limitedxe2x80x99 BMP""s, such as sand filters, water quality inlets, and, reservoir/vault type of structures. Space constraints, high property values, soil conditions, and the proximity of other building foundations often preclude the use of conventional, space-intensive stormwater BMP""s such as detention ponds. For in-fill construction or redevelopment in built-up urban areas, where pollutant loads from urban runoff are usually the greatest, unconventional stormwater treatment technologies may be necessary.
Vault-type treatment technologies have been widely used for stormwater treatment in urban areas; however, the effectiveness of these devices for removal of suspended solids and oil and grease has been only marginal. A great weakness of these types of devices has been that large storm events tend to flush out the system, thereby releasing pollutants that were previously removed.
Prior art in the field of this invention of which the applicant is aware includes the following:
U.S. Pat. No. 4,127,488, Bell, J. A. et al., November 1978, Method and apparatus for separating solids from liquids.
U.S. Pat. No. 4,136,010, Pilie, R. J. et al., January 1979, Catch basin interceptor.
U.S. Pat. No. 4,328,101, Broden, C. V., May 1982, Device for separating particulate matter from a fluid.
U.S. Pat. No. 4,363,731, Filippi, R., December 1982, Device for regulating the flow of waste waters.
U.S. Pat. No. 4,383,922, Beard, H. J., May 1983, Waste water clarifier.
U.S. Pat. No. 4,983,295, Lamb, T. J. et al., January 1991, Separator.
U.S. Pat. No. 4,985,148, Monteith, J. G., January 1991, Improved separator tank construction.
U.S. Pat. No. 5,004,534, Buzzelli, V., April 1991, Catch basin.
U.S. Pat. No. 5,186,821, Murphy, D. T., February 1993, Wastewater treatment process with cooperating velocity equalization, aeration, and decanting means.
U.S. Pat. No. 5,342,144, McCarthy, E. J., August 1994, Stormwater control system.
U.S. Pat. No. 5,520,825, Rice, W. M., May 1996, Oil-water separator.
U.S. Pat. No. 5,536,409, Dunkers, K. R., July 1996, Water treatment system.
U.S. Pat. No. 5,637,233, Earrusso, P. J., June 1997, Method and apparatus for separating grease from water.
U.S. Pat. No. 5,679,258, Petersen, R. N., October 1997, Mixed immiscible liquids collection, separation, and disposal method and system.
U.S. Pat. No. 5,759,415, Adams, T., June 1998, Method and apparatus for separating floating and non-floating particulate from rainwater drainage.
U.S. Pat. No. 5,788,848, Blanche, P. et al., August 1998, Apparatus and methods for separating solids from flowing liquids or gases.
U.S. Pat. No. RE30,793, Dunkers, K. R., November 1981, Apparatus for water treatment.
In addition to the patents listed above, a number of inventions in the general field of stormwater treatment methods and devices were discovered during the patent search. The inventions listed below have an element or elements similar to the invention disclosed herein; however, additional elements, details of elements, and/or applications of the inventions differ significantly from the forms and functions of the present invention. While the inventions listed below are intended to provide stormwater treatment, the principle of operation for many of these devices is filtration rather than sedimentation.
U.S. Pat. No. 4,298,471, Dunkers, K. R., November 1981, Apparatus for equalization of overflow water and urban runoff in receiving bodies of water.
U.S. Pat. No. 4,377,477, Dunkers, K. R., March 1983, Apparatus for equalization of overflow water and urban runoff in receiving bodies of water.
U.S. Pat. No. 4,664,795, Stegall, W. A. et al., May 1987, Two-stage waste water treatment system for single family residences and the like.
U.S. Pat. No. 4,747,962, Smissom, B., May 1988, Separation of components of a fluid mixture.
U.S. Pat. No. 4,865,751, Smissom, B., September 1989, Separation of components of a fluid mixture.
U.S. Pat. No. 5,080,137, Adams, T. R., January 1992, Vortex flow regulators for storm sewer catch basins.
U.S. Pat. No. 5,232,587, Hegemier, T. E. et al., August 1993, Stormwater inlet filters.
U.S. Pat. No. 5,322,629, Stewart, W. C., June 1994, Method and apparatus for treating stormwater.
U.S. Pat. No. 5,403,474, Emery, G. R., April 1995, Curb inlet gravel sediment filter.
U.S. Pat. No. 5,437,786, Horsley, S. W. et al., August 1995, Stormwater treatment system/apparatus.
U.S. Pat. No. 5,480,254, Autry, J. L. et al., January 1996, Storm drain box filter and method of use.
U.S. Pat. No. 5,549,817, Horsley, S. W. et al., August 1996, Stormwater treatment system/apparatus.
U.S. Pat. No. 5,702,593, Horsley, S. W. et al., December 1997, Stormwater treatment system/apparatus.
U.S. Pat. No. 5,707,527, Knutson, J. H. et al., January 1998, Apparatus and method for treating stormwater runoff.
U.S. Pat. No. 5,730,878, Rice, T., March 1998, Contaminated waste water treatment method and device.
U.S. Pat. No. 5,744,048, Stetler, C. C., April 1998, Clog resistant storm drain filter.
U.S. Pat. No. 5,770,057, Filion, G., June 1998, Overflow water screening apparatus.
U.S. Pat. No. 5,779,888, Bennett, P. J., July 1998, Filtering apparatus.
U.S. Pat. No. 5,810,510, Urriola, H., September 1998, Underground drainage system.
U.S. Pat. No. 5,840,180, Filion, G., November 1998, Water flow segregating unit with endless screw.
U.S. Pat. No. 5,890,838, Moore, Jr. Et al., April 1999, Stormwater dispensing system having multiple arches.
U.S. Pat. No. 5,972,216, Acernese, P. L. et al., October 1999, Portable multi-functional modular water filtration unit.
U.S. Pat. No. 5,985,157, Leckner, J. P. et al., November 1999, Filter device.
Previous vault or box type treatment devices used in wastewater or stormwater treatment applications acted as xe2x80x9cflow-throughxe2x80x9d systems. In these previous devices, incoming flows enter the device, take a given period of time based on baffles and size to flow through the device, and then exit the device. If flows were coming in continuously, they would enter and exit the device at the same flow rate. Previous devices have different systems within the vault to channel, divert, or reduce flow rates inside the vault in order to facilitate gravity separation. All of these devices are somewhat effective at settling out particles down to a certain size or specific gravity, but none of these devices are effective at removing the very small size range of particles that make up the majority of toxic pollutants in storm water runoff. These particles are typically in the 100-micron and smaller size range, and simply will not settle out of the water if there are horizontal flow velocities present.
Most currently available stormwater treatment devices are designed to reduce the concentrations of pollutants in stormwater by screen, filter or enhanced gravitational separation (i.e. swirl concentrators). However, such systems provide little or no detention capture volume to mitigate the runoff peaks for small or large runoff events. In other words, these systems function as flow-through devices, resulting in the lack of capture volume and overall poor treatment performance. Specifically, much of the settleable materials trapped or deposited during more numerous smaller runoff events are agitated and remobilized, and wash out of these devices when larger and more intense runoff events occur.
Properly sized and maintained wet detention ponds (retention ponds) provide some of the most effective stormwater treatment available. Because of site-specific limitations, however many desirable features of wet detention ponds are not utilized in real world conditions. Available surface area, possible thermal pollution, attractive nuisance liabilities, mosquitoes and long-term maintenance access and disposal are some of the difficulties that must be addressed with a surface pond.
This stormwater mitigation system solves these problems and more, and includes the benefits of a properly designed retention pond.
The apparatus advantageously settles particles down to a size of 100 microns and smaller out of suspension in the stormwater by utilizing a unique volume control design. The vault of the present invention is designed to treat a given volume of stormwater runoff, as opposed to a given runoff flow rate as treated in other devices. In so doing, the horizontal flows for the entire volume of water to be treated can be nearly eliminated, such that with a reduced flow rate very small particles may drop out of suspension and collect on the bottom of the vault. This is accomplished through a combination of physical space to capture and hold water to be treated, restriction of flow out of the apparatus at a slower flow rate than flow into the apparatus, and vertically stacked pools of water with reduced or eliminated relative flow velocity.
Features that are thought to provide such consistently high quality treatment advantageously include; a permanent pool (i.e., a pool essentially continuously present after it is first filled) to eliminate the resuspension of pollutants, extended quiescent settling conditions to promote retention of the Total Suspended Solids (xe2x80x9cTSSxe2x80x9d) and floatable materials, subsurface conditions that curtail the resuspension of deposited sediment, sufficient volume to retain runoff from the majority of runoff events and capture and treat the xe2x80x9cfirst flushxe2x80x9d of the larger events, flow control system to attenuate the runoff flow rates from the majority of storm events and prevent flushing of the captured pollutants, and large surface area that promotes oxygen transfer to reduce pollutant remobilization.
An aspect of this invention is to provide an apparatus for removal of pollutants with densities greater than and less than water from stormwater runoff.
Another aspect of this invention is to provide an apparatus that retains and immobilizes trapped pollutants, even during periods when flows are high.
Another aspect of this invention is to accumulate pollutants that are less and more dense than water until a time when the apparatus is cleaned out.
Another aspect of this invention is to minimize velocity in the vicinity of the bottom of the apparatus to minimize resuspension of deposited sediments and associated pollutants. The slower the velocity of water in at least part of the device, the more effective will be the removal of particles.
Another aspect of this invention is to provide an apparatus that can provide treatment of stormwater for larger tributary drainage areas by addition of modular sections.
Another aspect of this invention is to collect stormwater runoff and release it at a controlled rate over a specified period of time via an outflow opening.
Other aspects and advantages will become apparent hereinafter.
In one embodiment, the apparatus includes a by-pass manhole, apparatus chambers including a plurality of interior baffles, and a junction box. This apparatus, along with properly sized and installed ancillary appurtenances, will advantageously collect and hold floatable debris, runoff bed load particulate material, free oil and grease, settleable sediments and those dissolved pollutants including metals, nitrogen and phosphorus nutrients, and soluble organic compounds the may adsorb or adhere to the surface of sediments and organic debris in stormwater. This apparatus, properly installed and utilizing a properly sized outflow opening aperture installed within an outlet opening, can capture and control the release of site runoff, significantly reducing erosion and stream degradation due to urbanization of the riparian habitat, and helps restore pre-development runoff rates to urbanized areas.
In one embodiment, the apparatus is a below grade modular concrete stormwater control device that is designed to manage and treat stormwater runoff by diverting a predetermined capture volume (or water quality capture volume) into the apparatus. As would be understood by one of ordinary skill in the art, the capture volume is typically sized, for example, between the mean and the maximized runoff event as defined in xe2x80x9cUrban Runoff Quality Management,xe2x80x9d Water Environment Federation (WEF) Manual of Practice No. 23 and American Society of Civil Engineersxe2x80x9d (ASCE) Manual and Report on Engineering Practice No. 87. The capture volume is surcharged into detention storage (the active pool).
This capture is brought about by a volume control diversion weir that directs the design capture volume runoff into the apparatus with a minimum hydraulic loss into the apparatus. Any subsequent flow beyond that of the design capture volume is allowed to bypass the apparatus via a volume control diversion weir returning to the stormwater or runoff collection system and/or receiving waters.
During wet weather and periods of site runoff, the detention time of the capture volume may be optimized to promote quiescent sedimentation within the active pool whereby settable solid particles less than 100 microns in size with a specific gravity greater than water will descend and insoluble oil droplets and marginally buoyant debris will float to the surface.
One aspect of the invention is a rectangular chamber of variable length, width and height assembled in a modular fashion. The rectangular chamber contains a system of overflow and underflow baffles, both perpendicular to and oblique to the primary direction of flow from the inlet to the chamber to the outlet from the chamber, which are located at opposite ends of the rectangular chamber. The baffles in the chamber serve several purposes including: flow momentum and energy dissipation, creation of a tortuous flow path, retention and immobilization of pollutants less and more dense than water, minimization of resuspension of sediments, and minimization of remobilization of floatable pollutants into the water column. The primary process for pollutant removal is gravitational separation, which occurs while water is detained in the chamber.
A baffle configuration for minimization of resuspension of trapped sediments and associated pollutants was first conceptualized by the inventors and then optimized by iterative experimentation involving three dimensional velocity measurements and dye visualization for a plurality of baffle configurations using a geometrically and hydraulically scaled physical model. Baffle configurations were evaluated for both dynamic (chamber filling and draining) and steady-state (chamber full with inflow rate equal to outflow rate) conditions. This exhaustive experimentation indicates that the baffle configuration of the invention disclosed minimizes resuspension of fine and coarse sediments and associated pollutants to a degree that exceeds the capabilities of prior art. In addition, a trapezoidal underflow baffle, the shape of which was optimized during hydraulic experimentation, impedes material less dense than water from entering the outflow section and exiting the vault. The trapezoidal configuration has the advantage of decreasing the downward velocity of water approaching and then moving under the baffle and into the outlet section and, thereby, decreases the risk of entraining floatable pollutants trapped behind the trapezoidal baffle into the flow passing into the outlet section. As a result, the plurality of interior baffles and the weir configuration advantageously are designed to provide minimum re-suspension of settable solids from within the permanent pool.
In one aspect, the apparatus has an inlet that delivers water to the chamber from a tributary surface land area, either directly or via storm sewer system piping. Water entering the chamber passes through a system of underflow and overflow baffles both perpendicular to and oblique to the primary direction of flow from the inlet to the outlet, which is located at the end of the rectangular chamber opposite the inflow. As water enters the chamber, the water level in the chamber rises above the permanent pool water surface elevation, which normally is less than or equal to the elevation of the invert of the outflow opening. Outflow from the chamber is controlled by an opening that is sized to provide a specified time for the water in the chamber to drain from the elevation at which the chamber is full to the elevation of the permanent pool. When the rate of inflow is greater than the rate of outflow, the water level in the chamber will rise to the elevation at which the chamber is full. Once the chamber is full, any flow in excess of the outflow rate under full conditions will bypass the chamber via an overflow structure 294. When the rate of outflow is greater than the rate of inflow, the water surface elevation in the chamber will decrease at a rate controlled by the size of the outflow opening, and the water surface elevation will decrease to the elevation of the outflow opening invert, at which time outflow will cease. For convenience and brevity, this chamber inflow volume, as described in previous applications, is herein called a capture volume.
By slowly metering out storm runoff back to the external environment, the apparatus is of great benefit as it not only removes pollutants but also duplicates runoff conditions that exist prior to urban development. This prevents erosion of stream channels, and also prevents a discharge of rapidly flowing runoff that would simply pick up more sediment after treatment.
Another aspect of the invention is a stormwater treatment apparatus, including a receptacle adapted to receive water flowing from a surface drainage area, the receptacle having a bottom and a top, the receptacle having an inlet and an outlet, the inlet and the outlet being in fluid communication with one another; and at least one baffle positioned within the receptacle between the inlet and the outlet, the baffle extending from the bottom of the receptacle, a first portion of the baffle and the bottom of the receptacle forming an angle therebetween.
A stormwater treatment apparatus varies from other types of treatment apparatus, such as septic tanks, in that stormwater treatment apparatus must capture a wide variety of particles of different sizes and compositions in a pulsed hydraulics environment, as opposed to the more constant flow environment of a septic tank. A stormwater treatment apparatus also differs from septic tanks in that the goal is to permanently trap sediments and other pollutants less or more dense than water, rather than to degrade organic matter and other biodegradable substances and in that a stormwater treatment apparatus is much larger than septic tanks, desirably having a volume of at least 500 cubic feet, more desirably at least 600 cubic feet and, preferably, at least 750 cubic feet. Generally, this apparatus size advantageously is sized to include an active pool volume sufficient to treat the capture volume of the area being treated. Additionally, one vault or more than one vault maybe used, depending on the topography of the area being treated, and size of the vault(s) being used. Factors effecting the size and number of vaults used in the apparatus, besides capture volume, include manufacturing capability, transportability to site, modularity of apparatus, cost of construction and installation, site topography, ease of installation, and apparatus footprint.
The apparatus advantageously substantially reduces bottom velocities, thereby greatly reducing resuspension of sediments. In particular, the angle formed between the first portion of the baffle and the bottom of the receptacle is desirably between 30 and 60 degrees, at is desirably inclined in a downstream direction. Further, the height of the baffle is desirably at least two feet to limit the washing out of sediment. To facilitate manufacture and cleaning the baffle desirably includes a second portion, the second portion of the baffle extending from the bottom of the receptacle and forming an angle with the bottom of the receptacle, the angle being roughly 90 degrees.
The apparatus desirably includes an inlet baffle positioned between the inlet and the outlet, the inlet baffle spaced from said bottom and extending between generally opposing walls and an outlet baffle positioned between the inlet and the outlet, the outlet baffle spaced from said bottom and extending between generally opposing walls of the receptacle. The lower end of the outlet baffle is desirably positioned below said outlet. The outlet baffle advantageously may define a horizontal cross-section between a first baffle extending from said bottom and said outlet baffle larger than the horizontal cross-section between said first baffle and a vertical plane tangent to an upstream side of said outlet baffle. This has the effect of reducing the velocity of fluid. In this regard, it is desirable that outlet baffle defines a center section and at least one outer section which extends toward said outlet from said center section. Advantageously, however, the spaces between the outlet baffle and the opposing walls are sufficiently large to permit cleaning and to facilitate manufacture.
Yet another aspect of the invention is an apparatus for cleaning stormwater runoff, the apparatus including a vault having a top, a bottom, two sides, a front and a back, the vault comprising a first baffle extending from the bottom of the vault; a second baffle extending from the bottom of the vault, an inlet section having an opening and an outlet section having an outlet opening.
The apparatus also advantageously includes vertically stacked columns of water, defined by, in one embodiment, varying horizontal flow rates and bounded by baffles creating regions of lower horizontal flow rate. When the vault is filling or full, there is a column of water, called for convenience an xe2x80x9cactive pool,xe2x80x9d that is filling via the inlet, draining via the outlet, or both. This pool is the water being held, treated, and released by the invention. As the active pool is treated, sediments settle to the floor of the vault. As a result, when there is water in the active pool, it has a significantly higher velocity than the water in the permanent pool. A typical flow velocity for the active pool is two to three feet per second.
In order to retain sediments and to prevent them from running out of the vault as it empties, and in order to prevent resuspension of the sediments as the vault refills at a later time, the apparatus advantageously includes a permanent pool. The permanent pool sits immediately below the active pool and receives most or all sediments as they drop out of the active pool. Due to the shape, design and spacing of the baffles surrounding and within the permanent pool and active pool, the permanent pool is an inactive pool (a permanent pool that has minimal to no flow velocity.) Based on tests, the inactive permanent pool of the preferred embodiment of this invention maintains flow velocities typically below 0.15 feet per second.
One of the failings of prior xe2x80x9cflow-throughxe2x80x9d systems was their inability to settle small particles from smaller storm flows without resuspending those particles in later large storm flows due to turbulence and currents that reach all areas of the prior vaults. The present apparatus, by creating an active pool that fills, holds and drains immediately above an inactive permanent pool, eliminates small particle re-suspension. Even in prior systems, simply applying baffles to create a physical barrier to sediments moving horizontally through the system, without creating a permanent pool, is only effective for larger, heavier particles: in prior flow-through systems, smaller and finer particles, which form the majority of toxic pollutants, are left without an inactive permanent pool area to reside in and are simply suspended (or re-suspended) in the flow as it moves from compartment to compartment and exits.
A further advantage of vertically stacked pools including a permanent pool is that of maintaining a compact footprint or plan area. By both treating the incoming volume of water and storing sediments in the same plan area more water volume can be treated on a given site.
Finally, the present invention advantageously includes an overflow structure, in one embodiment integral to the outlet section of the vault. When inflow of stormwater exceeds the volume capacity of the treatment system, the overflow structure diverts excess stormwater flow without substantially effecting the ability of the system to effectively treat the full volume of stormwater already in the vault.